Analyte sensors facilitate the sensing of certain conditions within a patient. Electrochemical sensors are commonly used, for example, to monitor blood glucose levels in the management of diabetes. In one scheme, a sensor having an anode and a cathode is inserted through the skin so that it is surrounded by interstitial fluid. A portion of the sensor exits the skin, remaining outside the body, where electrical connections to the anode and the cathode may be made. Ensuring that a suitable electrical connection is made and is maintained is a challenge of such systems. An electronic measuring device outside the body may be used to measure electrical current from the sensor for recording and display of a glucose value. These types of devices are described, for example, in U.S. Pat. No. 5,965,380 to Heller et al. and U.S. Pat. No. 5,165,407 to Ward et al.
In addition to electrochemical glucose sensors, a number of other electrochemical sensors have been developed to measure the chemistry of blood or other body fluids or materials. Electrochemical sensors generally make use of one or more electrochemical processes and electrical signals to measure a parameter. Other types of sensors include those that use optical techniques to perform a measurement.
Although some of these devices are slender and flexible thus increasing patient comfort, such devices are difficult to insert through the skin. Unlike a typical hypodermic needle, such devices are too fragile and flexible to be simply pushed through the skin surface using normal force and speed. When the tip of such a device is forced against the skin, the device may bend and buckle with much less force than would be required to achieve skin penetration.
Current art provides several approaches for insertion of such slender flexible devices through the skin. In one case, the device is placed coaxially inside a hollow tube with a sharpened end, such as a hypodermic needle or trocar. The needle is inserted through the skin with the device inside. As a second step, the needle is withdrawn, leaving the device behind, passing through the skin into the body. See, for example, U.S. Pat. No. 6,695,860 to Ward et al. The insertion process may be painful, due to the large diameter needle, and a larger opening is made in the skin than required for passing the device alone, increasing trauma and the possibility of infection.
In a variation of this approach, the functions of the device are incorporated into a thin needle which must stay inserted into the skin. The needle provides additional mechanical strength and a sharpened point to assist in piercing the skin. However, due to its larger size and rigidity, this approach also contributes to patient discomfort for the duration of the insertion. See, for example, U.S. Pat. No. 6,501,976.
In addition, the presence of a rigid needle places mechanical constraints on the size and shape of the device housing that is attached to the surface of the skin where the device exits the skin. The needle also must be treated as a biohazard “sharp” since it is capable of transmitting disease if it should accidentally puncture the skin of another individual after being used in device insertion.